The overall objective of this proposal is to determine the molecular mechanism(s) by which luteinizing hormone (LH) regulates ovarian function. Through binding to specific cell surface receptors, LH plays an essential role in ovarian follicular development, ovulation, and subsequent maintenance and function of resulting corpora lutea. By these means LH controls fertility, implantation and early pregnancy. The objective of this proposal is to identify and characterize molecular mechanisms responsible for these actions. Specifically, these studies will focus on the post-transcriptional and post-translationaI events involved in the regulation of LH/hCG receptor expression. To accomplish this, three specific aims are proposed. Aim l will examine the novel proposal that LH/hCG receptor (LHR) gene expression is regulated post- transcriptionalIy. In particular, we propose to identify structural components of the LHR mRNA that determine the post-transcriptionaI control of LHR mRNA expression, including its stability and translationaI efficiency. These studies will utilize constructs of the 3' -untranslated region of LHR cDNA in transfected cells and chimeric constructs with a reporter gene. Aim 2 will determine the role of an LH/hCG receptor mRNA binding protein (LR/BP) on the expression of the LHR gene. These studies will determine the site of the interaction of this protein on the LHR mRNA and examine the role of this protein on LHR mRNA stability. The latter studies on the destabilization of the LHR mRNA will be facilitated by our development of an in vitro decay system employing polyribosomes from the rat ovary, in which we demonstrated hCG-induced down-regulation of LHR mRNA. Aim 3 will examine the role of posttranslationaI modification of the LH/hCG receptor on its trafficking to the plasma membrane. Using mutant receptors which lack the ability to undergo post- translationaI modification, the sites of post-translationaI processing and the role of these modifications on the insertion of the functional receptors on the plasma membrane will be examined.The proposed studies address novel questions central to reproductive endocrinology and are directly relevant to the diagnosis and treatment of infertility.